Microstructured adhesive articles have been prepared by applying a flowable pressure sensitive adhesive to the surface of a microstructured release liner or the surface of a microstructured molding tool. The process results in the creation of an adhesive having a microstructured surface. When the resulting articles are dry laminated under pressure to substrates such as glass or polymer films, the microstructural features created in the adhesive surface allow air to escape from the bonding interface, thereby minimizing or preventing the formation of bubbles and pinholes.
During lamination, the microstructural features may flatten out and wet the substrate surface. Typically, applied pressure is used to collapse the structures during lamination and form the adhesive bond. However, this process introduces stresses into the adhesive as the adhesive relaxes and tries to return to its initial microstructured state. These stresses can create defects in the adhesive that adversely affect its adhesive and optical properties.
A variety of techniques have been used to prepare adhesive articles with microstructured surfaces. Typically the adhesive surface is contacted to a structured tool or release liner to form a structured pattern in the adhesive layer. For example, in U.S. Pat. No. 6,315,651 (Mazurek et al.) microstructured pressure sensitive adhesives are formed by molding an adhesive layer against a microstructured tool or a microstructured liner, and in US Patent Publication No. 2006/0188704 (Mikami et al.) fluid egress structures are formed in an adhesive surface by contacting the adhesive to a structured release tool or a structured release liner. Japanese Utility Model Publication 7-29569 (Kawada et al.) describes forming a tack label for a container such as a bottle. The tack label is readily removable from the bottle surface by soaking the bottle in an aqueous solution, because the adhesive contains an uneven shape to form penetration channels permitting fluid entry to the bond line. The labels are formed by contacting an adhesive to a structured release liner, the release liner having been formed by embossing, and then contacting the label material to the exposed adhesive surface. Additionally, in US Patent Publication No. 2007/0212635 (Sherman et al.), a structured adhesive surface is formed by pressing a microstructured tool or release liner to a crosslinked adhesive surface.
U.S. Pat. No. 5,266,228 (Orr), describes a double-sided adhesive-coated foam tape in which the grooves are fine enough that upon bonding the grooves largely or completely disappear. In Japanese Patent Publication 7-138541 (Shimizu), an adhesion process film is prepared with an embossing process to form fine continuous concave grooves.
In addition, several applications have been described in which microstructured adhesive layers have beads or pegs that protrude from the adhesive surface to make the adhesive surface positionable or repositionable upon contact with a substrate surface. U.S. Pat. No. 5,296,277 (Wilson et al.) describes such a system. U.S. Pat. No. 7,060,351 (Hannington), describes an adhesive article that provides air egress, by providing an area of no initial adhesion for the air to flow out from under the construction. In the article, a continuous layer of adhesive is adhered to a surface that has a plurality of spaced-apart non-adhesive material, and the non-adhesive material becomes embedded in the adhesive layer.